A list of one or more classification flags or null
Remarks
PointCloudFilterDefinition uses classification codes, return values, and
classification flags to filter the point cloud data being rendered. Classification
codes are used to define the type of surface, or surfaces, that reflected the lidar pulse.
Return values correspond to the value stored in the RETURNS field of a point cloud
and are typically influenced by the height of each surface that was scanned.
Classification flags are a secondary description of the lidar pulses (in addition to
their classification code).